The best thing you can do for this user is to teach him how SO works and having that answer deleted is one pretty straightforward way of doing it. Comments and explanations are not required, but very welcome indeed.
So flag it and - if you feel like - add a nice comment explaining the reasons why that's an invalid answer, perhaps pointing to the help page How to Answer, which is pretty clear about it
Pay it forward
Saying “thanks” is appreciated, but it doesn’t answer the question. Instead, vote up the answers that helped you the most! If these answers were helpful to you, please consider saying thank you in a more constructive way – by contributing your own answers to questions your peers have asked here.
As noted in the comments, we also have the magic link
[answer]. Typing it in a comment will result in a link to the help page mentioned above.
Finally, it's also worth noting that there's no reputation limit for seeing your own deleted answers, as discussed here, and in case the answer was deleted by someone else a link to the FAQ is also added.